Methane’s abundance and low cost makes it an optimal raw material for chemical precursors and other energy dense fuels. Traditional methods of converting methane to methanol require large amounts of energy through thermal catalysis and high capital costs. However, electrochemical oxidation of methane is a cleaner and cheaper way to produce methanol, and a systematic study of an electrochemical cell could help assure selectivity over undesired products. Electrochemical oxidation of methane is an underdeveloped field, but electrochemical cells have been employed with high selectivity towards methanol. [1,2] Promising transition state metal-oxide catalysts have shown activity towards the selectivity of methanol over other by products, such as carbon dioxide, carbon monoxide, formic acid, formaldehyde. [2, 3] Further investigation of single site metal oxide catalysts is required to improve conversion and activity, but system optimization is also required. Reports of electrolyzer and fuel cell systems show varying assemblies, ranging from various solid and liquid electrolytes, temperatures, pressures, and current densities. [1-3] Few reports have been consistent on the operating current density and potential windows of such systems. Little work has been done on understanding how various components for these systems and understanding the phenomena of creating methanol in this partial oxidation pathway. In this study, we explore the activity, selectivity, efficiency of transition metal oxide catalyst in operation in an electrolyzer. The electrolyzer used was tested under a variety of relative humidity, operating temperatures, current densities, and membrane electrode assemblies. Through electrochemical and conductivity measurements, and gas phase analysis of the effluent, a better understanding of the partial electrochemical oxidation of methane to methanol is elucidated. The results of this study provide a systematic approach to this challenging problem and provide insights on new catalyst and electrochemistry pathways. References: Tomita, A., et. al., Direct Oxidation of Methane to Methanol at Low Temperature and Pressure in an Electrochemical Fuel Cell . Angewandte Chemie International Edition, 2008. 47 : p. 1462–1464. Lee, B., et. al., Direct oxidation of methane to methanol over proton conductor/metal mixed catalysts , Journal of Catalysis, 271( 2): p. 195-200. Rocha, R.S., et. al., Electrosynthesis of methanol from methane: The role of V2O5 in the reaction selectivity for methanol of a TiO2/RuO2/V2O5 gas diffusion electrode . Electrochimica Acta, 2013. 87: p. 606-610.

Abstract The 2020 Sturgis motorcycle rally resulted in widespread transmission of severe acute respiratory syndrome coronavirus 2 across the United States. At least 649 coronavirus disease 2019 cases were identified, including secondary and tertiary spread to close contacts. To limit transmission, persons attending events should be vaccinated or wear masks and practice physical distancing if unvaccinated. Persons with a known exposure should be managed according to their coronavirus disease 2019 vaccination or prior infection status and may include quarantine and coronavirus disease 2019 testing.

Abstract Acidic zeolites are effective catalysts for the cracking of large hydrocarbon molecules into lower molecular weight products required for transportation fuels. However, the ways in which the zeolite structure affects the catalytic activity at Brønsted protons are not fully understood. One way to characterize the influence of the zeolite structure on the catalysis is to study alkane cracking and dehydrogenation at very low conversion, conditions for which the kinetics are well defined. To understand the effects of zeolite structure on the measured rate coefficient (k app ), it is necessary to identify the equilibrium constant for adsorption into the reactant state (K ads‐H+ ) and the intrinsic rate coefficient of the reaction (k int ) at reaction temperatures, since k app is proportional to the product of K ads‐H+ and k int . We show that K ads‐H+ cannot be calculated from experimental adsorption data collected near ambient temperature, but can, however, be estimated accurately from configurational‐bias Monte Carlo (CBMC) simulations. Using monomolecular cracking and dehydrogenation of C 3 –C 6 alkanes as an example, we review recent efforts aimed at elucidating the influence of the acid site location and the zeolite framework structure on the observed values of k app and its components, K ads‐H+ and k int .

A detailed investigation was conducted on the factors influencing the properties of silica-supported tungsten oxide catalysts for propene metathesis. A principal goal of this work was to identify the processes involved in the formation of catalytically active sites. To probe the influence of dispersion, samples were prepared across a range of W loadings using two methods of catalyst preparation: incipient wetness impregnation of amorphous silica and ion exchange of mesoporous SBA-15. The samples were characterized by nitrogen adsorption, UV-vis, Raman, and X-ray absorption spectroscopy (XAS). Catalytic activity was observed to increase with W surface concentration up to the point where WO<sub>3</sub> nanoparticles formed. The catalytic performance of all samples was enhanced 2-fold by pretreatment in He, in comparison to pretreatment in air. In situ characterization of samples pretreated in He by Raman and XAS shows an increase in the relative concentration of isolated dioxo W(6+) species relative to mono-oxo W(6+) species, and in situ XAS data collected during propene metathesis indicated that a similar conversion occurs for air-pretreated samples in the presence of propene. For both air- and He-pretreated catalysts an activation period was observed, during which the activity increased and attained steady-state activity. This period was significantly longer for air-pretreated catalysts and was accompanied by the transient formation of acetone. While acetone was not observed during the much shorter transient of He-pretreated samples, in situ XAS provided evidence of reduction occurring in these samples upon contact with propene. In conclusion, it is also notable that, independent of the manner of catalyst preparation or pretreatment, the rate of propene metathesis is first order in propene and exhibits an activation energy of 200 kJ/mol. A model is proposed to explain why only a fraction of the isolated tungstate species is active for propene metathesis (~5%) and why this fraction increases with increasing concentration of W dispersed on silica.

The electrochemical reduction of carbon dioxide using renewably generated electricity offers a potential means for producing fuels and chemicals in a sustainable manner. To date, copper has been found to be the most effective catalyst for electrochemically reducing carbon dioxide to products such as methane, ethene, and ethanol. Unfortunately, the current efficiency of the process is limited by competition with the relatively facile hydrogen evolution reaction. Since multi-carbon products are more valuable precursors to chemicals and fuels than methane, there is considerable interest in modifying copper to enhance the multi-carbon product selectivity. Here, we report our investigations of electrochemical carbon dioxide reduction over CuAg bimetallic electrodes and surface alloys, which we find to be more selective for the formation of multi-carbon products than pure copper. This selectivity enhancement is a result of the selective suppression of hydrogen evolution, which occurs due to compressive strain induced by the formation of a CuAg surface alloy. Furthermore, we report that these bimetallic electrocatalysts exhibit an unusually high selectivity for the formation of multi-carbon carbonyl-containing products, which we hypothesize to be the consequence of a reduced coverage of adsorbed hydrogen and the reduced oxophilicity of the compressively strained copper. Thus, we show that promoting copper surface with small amounts of Ag is a promising means for improving the multi-carbon oxygenated product selectivity of copper during electrochemical CO₂ reduction.

Many multicomponent materials exhibit significant configurational disorder. Diffusing ions in such materials migrate along a network of sites that have different energies and that are separated by configuration dependent activation barriers. We describe a formalism that enables a first-principles calculation of the diffusion coefficient in solids exhibiting configurational disorder. The formalism involves the implementation of a local cluster expansion to describe the configuration dependence of activation barriers. The local cluster expansion serves as a link between accurate first-principles calculations of the activation barriers and kinetic Monte Carlo simulations. By introducing a kinetically resolved activation barrier, we show that a cluster expansion for the thermodynamics of ionic disorder can be combined with a local cluster expansion to obtain the activation barrier for migration in any configuration. This ensures that in kinetic Monte Carlo simulations, detailed balance is maintained at all times and kinetic quantities can be calculated in a properly equilibrated thermodynamic state. As an example, we apply this formalism for an investigation of lithium diffusion in ${\mathrm{Li}}_{x}{\mathrm{CoO}}_{2}.$ A study of the activation barriers in ${\mathrm{Li}}_{x}{\mathrm{CoO}}_{x}$ within the local density approximation shows that the migration mechanism and activation barriers depend strongly on the local lithium-vacancy arrangement around the migrating lithium ion. By parametrizing the activation barriers with a local cluster expansion and applying it in kinetic Monte Carlo simulations, we predict that lithium diffusion in layered ${\mathrm{Li}}_{x}{\mathrm{CoO}}_{2}$ is mediated by divacancies at all lithium concentrations. Furthermore, due to a strong concentration dependence of the activation barrier, the predicted diffusion coefficient varies by several orders of magnitude with lithium concentration x.

We describe catalytic sequences for converting biomass-derived carboxylic acids, to fuels and lubricants that are compatible with the existing energy infrastructure.

ConspectusHighly dispersed transition-metal Lewis acid centers (e.g., Zn, Co, Y, La, Fe, Sn, Hf, and Zr) and Lewis acid-anchored noble metal centers (e.g., Pt–Zn, Pt–Sn, Pt–Fe, Rh–Zn, and Rh–Co) supported on siliceous zeolites are promising catalysts for a number of industrially important reactions, such as alcohol dehydrogenation, aldol condensation, alkane dehydrogenation, and olefin hydroformylation. In this Account, we describe the preparation and characterization of Lewis acid centers grafted onto hydrogen (H)-bonded silanol groups present in zeolites as well as Lewis acid-anchored noble metal centers and discuss the mechanism and kinetics for different reactions occurring over each type of center. We show that isolated and nested Lewis acid centers can be created by the reaction of hydrated cationic species with H-bonded silanol groups on dealuminated beta (DeAlBEA) or Silicalite-1 zeolite. We then demonstrate that isolated and nested Lewis acid centers are effective catalysts for light alkane dehydrogenation. Nested Lewis acid centers can also serve as efficient anchoring sites for dispersing noble metals such as Pt and Rh to generate bimetallic centers that exhibit superior catalytic performance relative to monometallic Pt and Rh for reactions such as alkane dehydrogenation and olefin hydroformylation. Finally, we summarize our recent investigations of isolated and nested Lewis acid centers and the Pt- and Rh-based bimetallic centers as catalysts for ethanol conversion to 1,3-butadiene (ETB), acetone conversion to isobutene (ATI), propane dehydrogenation to propene (PDH), n-butane dehydrogenation to butene and 1,3-butadiene (BDH), and ethene hydroformylation to propanal. We show that the activity of Lewis acid centers for these reactions is affected by their local coordination environments. In particular, we highlight the significance of H-bonding between hydroxyl groups connected to Lewis acid centers in an open configuration (M–OH) and silanol groups on zeolite supports to generate (≡SiO)xMn+–OH···(O(H)–Si≡)y structures, which exhibit aldol condensation activities that are higher than that of (≡SiO)xMn+–OH sites. These studies demonstrate that siliceous zeolites rich in H-bonded silanol groups can be utilized to create highly dispersed Lewis acid centers and can be further employed as an anchoring platform for noble metal atoms to construct atomically dispersed bimetallic centers. Both the chemical structure and the local coordination environment of these centers significantly influence their catalytic performance.

Growing concern with the environmental impact of CO₂ emissions produced by combustion of fuels derived from fossil-based carbon resources has stimulated the search for renewable sources of carbon. Much of this focus has been on the development of methods for producing transportation fuels, the major source of CO₂ emissions today, and to a lesser extent on the production of lubricants and chemicals. First-generation biofuels such as bioethanol, produced by the fermentation of sugar cane- or corn-based sugars, and biodiesel, produced by the transesterification reaction of triglycerides with alcohols to form a mixture of long-chain fatty esters, can be blended with traditional fuels in limited amounts and also arise in food versus fuel debates. Producing molecules that can be drop-in solutions for fossil-derived products used in the transportation sector allows for efficient use of the existing infrastructure and is therefore particularly interesting. In this context, the most viable source of renewable carbon is abundantly available lignocellulosic biomass, a complex mixture of lignin, hemicellulose, and cellulose. Conversion of the carbohydrate portion of biomass (hemicellulose and cellulose) to fuels requires considerable chemical restructuring of the component sugars in order to achieve the energy density and combustion properties required for transportation fuels-gasoline, diesel, and jet. A different set of constraints must be met for the conversion of biomass-sourced sugars to lubricants and chemicals. This Account describes strategies developed by us to utilize aldehydes, ketones, alcohols, furfurals, and carboxylic acids derived from C₅ and C₆ sugars, acetone-butanol-ethanol (ABE) fermentation mixtures, and various biomass-derived carboxylic acids and fatty acids to produce fuels, lubricants, and chemicals. Oxygen removal from these synthons is achieved by dehydration, decarboxylation, hydrogenolysis, and hydrodeoxygenation, whereas reactions such as aldol condensation, etherification, alkylation, and ketonization are used to build up the number of carbon atoms in the final product. We show that our strategies lead to high-octane components that can be blended into gasoline, C₉-C₂₂ compounds that possess energy densities and properties required for diesel and jet fuels, and lubricants that are equivalent or superior to current synthetic lubricants. Replacing a fraction of the crude-oil-derived products with such renewable sources can mitigate the negative impact of the transportation sector on overall anthropogenic greenhouse gas (GHG) emissions and climate change potential. While ethanol is a well-known fuel additive, there is significant interest in using ethanol as a platform molecule to manufacture a variety of valuable chemicals. We show that bioethanol can be converted with high selectivity to butanol or 1,3-butadiene, providing interesting alternatives to the current production from petroleum. Finally, we report that several of the strategies developed have the potential to reduce GHG emissions by 55-80% relative to those for petroleum-based processes.

Electrolyte cation size is known to influence the electrochemical reduction of CO₂ over metals; however, a satisfactory explanation for this phenomenon has not been developed. We report here that these effects can be attributed to a previously unrecognized consequence of cation hydrolysis occurring in the vicinity of the cathode. With increasing cation size, the pK_a for cation hydrolysis decreases and is sufficiently low for hydrated K⁺, Rb⁺, and Cs⁺ to serve as buffering agents. Buffering lowers the pH near the cathode, leading to an increase in the local concentration of dissolved CO₂. The consequences of these changes are an increase in cathode activity, a decrease in Faradaic efficiencies for H₂ and CH₄, and an increase in Faradaic efficiencies for CO, C₂H₄, and C₂H₅OH, in full agreement with experimental observations for CO₂ reduction over Ag and Cu.